Mining Sia coin on Ubuntu

Sia is a hot crypto-currency for miners.  Just a week ago, the sia network hashrate was 6.5 Th/s, and the only way to mine was solo as there were no public pools.  In the last three days, sia.nanopoool.org, and siamining.com started up and the network hashrate grew to 14.7 Th/s, with the two pools making up 80% of the total network hashrate.

Mining on Windows is relatively easy, with nanopool posting a binary build of siamining's gominer fork.  For Ubuntu, you need to build it from the source.  For that, you'll need to install go first.  If you type 'go' in Ubuntu 14.04, you'll get the following message:
The program 'go' is currently not installed. You can install it by typing:
apt-get install gccgo-go

I tried the similar package 'gccgo', which turned out to be a rabbit hole.  The version 1.4.2 referred to in the gominer readme is a version of the package 'golang'.  Neither gccgo-go or gccgo have the latest libraries needed my gominer.  And the most recent version of golang in the standard Ubuntu repositories is 1.3.3.  However the Ethereum foundation publishes a 1.5.1 build of golang in their ppa.

Even with the golang 1.5.1, building gominer wasn't as simple as "go get github.com/SiaMining/gominer".  The reason is that the gominer modifications to support pooled mining are in the "poolmod3" branch, and there is no option to install directly from a branch.  So I made my own fork of the poolmod3 branch, and added detailed install instructions for Ubuntu:

add-apt-repository -y ppa:ethereum/ethereum
sudo apt-get update
apt-get install -y git ocl-icd-libopencl1 opencl-headers golang
go get github.com/nerdralph/gominer-nr

Once I got it running on a single GPU, I wanted to find out if it was worthwhile to switch my eth mining rigs to sia.  I couldn't find a good sia mining calculator, so I pieced together some information about mining rewards and used the Sia Pulse calculator.  I wanted to compare a single R9 290 clocked at 1050/1125, which gets about 29Mh/s mining eth, earning $2.17/day.  For Sia, the R9 290 gets about 1100Mh, which if you put that into the Sia Pulse calculator along with the current difficulty of 4740Th, it will calculate daily earnings of 6015 SC/day.  Multiplying by the 62c/1000SC shown on sia.nanopool.org will give you a total of $3.73/d, but that will be wrong.  The Sia Pulse calculator defaults to a block reward of 300,000, but that goes down by 1 for each block.  So at block 59,900, the block reward is 240,100. and the actual earnings would be $2.99/d.

Since the earnings are almost 40% better than eth, I decided to switch my mining rigs from eth to sia.  I had to adjust the overclocking settings, as sia is a compute-intensive algorithm instead of a memory-intensive algorithm like ethereum.  After reducing the core clock of a couple cards from 1050 to 1025, the rigs were stable.  When trying out nanopool, I was getting a lot of "ERROR fetching work;" and "Error submitting solution - Share rejected" messages.  I think their servers may have been getting overloaded, as it worked fine when I switched to siamining.com.  I also find siamining.com has more detailed stats, in particular % of rejected shares (all below 0.5% for me).

I may end up switching back to eth in the near future, since a doubling in network hashare for sia will eventually mean a doubling of the difficulty, cutting the amount of sia mined in half.  In the process I'll at least have learned a bit about golang, and I can easily switch between eth and sia when one is more profitable than the other.